An emulsion is an intimate mixture of two liquid phases, such as oil and water, in which the liquids are mutually insoluble and where either phase may be dispersed in the other. An oily waste emulsion, in which oil is dispersed in the water phase, may contain any of various types of oil in a wide range of concentrations. These oils are defined as substances that can be extracted from water by hexane, carbon tetrachloride, chloralform, or fluorocarbons. In addition to oils, typical contaminants of these emulsions may be solids, silt, metal particles, emulsifiers, cleaners, soaps, solvents, and other residues. The types of oils found in these emulsions will depend on the industry. They may be fats, lubricants, cutting fluids, heavy hydrocarbons such as tars, grease, crude oils, and diesel oils, and also light hydrocarbons including gasoline, kerosene, and jet fuel. Their concentration in the wastewater may vary from only a few parts per million to as much as 5 to 10%, by volume.
A stable oil-in-water emulsion is a colloidal system of electrically charged oil droplets surrounded by an ionic environment. Emulsion stability is maintained by a combination of physical and chemical mechanisms.
Emulsions may be broken by chemical, electrolytic, or physical methods. The breaking of an emulsion is also called resolution, since the aim is to separate the original mixture into its parts. Chemicals are commonly used for the treatment of oily wastewaters, and are also used to enhance mechanical treatment. In breaking emulsions, the stabilizing factors must be neutralized to allow the emulsified droplets to coalesce. The accumulated electric charges on the emulsified droplet are neutralized by introducing a charge opposite to that of the droplet. Chemical emulsion breakers provide this opposite charge.
The treatment of oily wastewater is normally divided into two steps, i.e., coagulation which is the destruction of the emulsifying properties of the surface active agent or neutralization of the charged oil droplet, and flocculation which is the agglomeration of the neutralized droplets into large, separable globules.
Traditionally, sulfuric acid has been used in oily waste treatment plants as the first step in emulsion breaking. Acid converts the carboxyl ion in surfactants to carboxylic acid, allowing the oil droplets to agglomerate. Chemical coagulating agents, such as salts of iron or aluminum, can be used in place of acid, with the additional benefit that these aid in agglomeration of the oil droplets. However, the aluminum or iron forms hydroxide sludges that are difficult to dewater. Acids generally break emulsions more effectively than coagulant salts, but the resultant acidic wastewater must be neutralized after oil/water separation.
Some examples of inorganic emulsion breakers useful in oil-in-water emulsions are: polyvalent metal salts such as alum, AlCl.sub.3, FeCl.sub.3, and Fe.sub.2 (SO.sub.4).sub.3, mineral acids such as H.sub.2 SO.sub.4, HCl, and HNO.sub.3, and adsorbents such as pulverized clay and lime.
Organic demulsifiers are extremely effective emulsion breaking agents, giving more consistent results and producing better effluent quality than an inorganic program. In many treatment plants, organic emulsion breakers have replaced traditional alum treatment for exactly those reasons. In addition to yielding a better quality effluent, organic emulsion breakers often require lower dosages than a corresponding inorganic treatment. Organic emulsion breakers reduce the amount of sludge generated in a treatment program by as much as 50 to 75%.
Some examples of organic emulsion breakers useful in oil-in-water systems are polyamines, polyacrylates and their substituted copolymers.
The present inventors have discovered through extensive experimentation that hydrophobically modified diallyldimethylammonium chloride (DADMAC) polymers assist in removing oil from various wastewater effluents contaminated with up to 5% oil. The clarity of the treated effluents was excellent, e.g., the untreated water had a turbidity of &gt;2,000 NTU and the water treated with the demulsifier according to the present invention had a turbidity of approximately 20 NTU. Moreover, poly(DADMAC) alone demonstrated no significant demulsification activity; whereas hydrophobically modified DADMAC polymers exhibited substantial demulsification activity.
Furthermore, the hydrophobically modified DADMAC demulsifier of the present invention is an all organic treatment which is an attractive alternative when it is undesirable to use an inorganic treatment.
The present invention also provides many additional advantages which shall become apparent as described below.